The present invention relates to a novel process for the preparation of ethercarboxylic acids by 1) adding alcohols to tertiary-alkyl esters of .alpha.,.beta.-unsaturated carboxylic acids to form the .beta.-ethercarboxylate, followed by 2) acid hydrolysis of the .beta.-ethercarboxylate to form the ethercarboxylic acid.
German 212,733 describes a process for the preparation of 3-alkoxypropionates by reacting methyl acrylate with lower monoalcohols in the presence of Ni acetoacetonate and butyllithium. European application 254,291 describes a process for the preparation of optionally substituted 3-alkoxypropionates by reacting monoalcohols or diols with optionally substituted acrylates in the presence of anionic ion exchangers which are present in the basic form. The European application 291,207 describes 3-alkoxypropionic acids, prepared by reacting aliphatic diols or alkoxylation products of aliphatic diols with acrylonitrile in DMF and subsequent hydrolysis of the 3-alkoxypropionitrile which is obtained.
Although the process products in the publications mentioned are intermediates for the preparation of .beta.-ethercarboxylic acids, all these methods have the disadvantage that their commercial application is very difficult. Thus, in the German Application 212,733, the recommended catalysts are relatively expensive and, in addition, it is very difficult and complicated to remove them from the corresponding addition compounds. The process is also restricted to monoalcohols as starting materials. The process according to the European Application 254,291 is restricted to monoalcohols and diols. In addition, a large excess of the alcohol component, with respect to the .alpha.,.beta.-unsaturated carboxylic acid, is required in order to produce an acceptable degree of conversion.
Similarly, the process in European Application 291,207 is restricted to the use of diols, along with the additional disadvantage that here dimethylformamide is required as the solvent and this can be removed from the addition product only with great difficulty. Also, hydrolysis of the intermediate product obtained can cause problems. If concentrated hydrochloric acid is used in excess, such as is described in European Application 291,207, then undesired ether decomposition reactions must be expected to take place during hydrolysis. However, if the hydrolysis is performed in the presence of strong bases such as sodium or potassium hydroxide, then at least equivalent amounts of bases are required, which produces correspondingly large amounts of salt when subsequently releasing the acids by neutralization, for example, with hydrochloric acid.
Incidentally, in all the methods in the prior art mentioned which use either methyl or ethyl (meth)acrylates, it is a common factor that undesired side reactions proceed via transesterification of the acrylate used, with the release of methanol or ethanol. The released methanol or ethanol can again add on to the acrylate used. Obviously, this amounts to a further undesired side reaction.